Killer factor is a cytoplasmically inherited genetic determinant in the yeast Saccharomyces cerevisiae that confers upon its host cells ("killers") the ability to secrete several toxic glycoproteins that kill sensitive cells. Killer factor is associated with two double-stranded RNAs (dsRNAs), which are found cytoplasmically separately encapsidated in virus-like particles (VLPs). These two dsRNAs are L, of 2.5 x 10 to the 6th power daltons, and M, of 1.4 x 10 to the 6th power daltons. L probably encodes the VLP polypeptides and M the polypeptides of the toxic glycoproteins. Mutants which lack all but a small portion of M also have their small (S) dsRMAs encapsidated in VLPs. Knowledge of the 5' and 3' end group structures of the killer factor RNAs is prerequisite to understanding their replication, transcription and translation. We presently know the ultimate 5' nucleotides of two of the dsRNAs (L and M) and one 3' end of two others (S1 and S3). We will extend the 5' sequences by polynucleotide kinase labelling. S1 appears to be tandem duplication of S3, as judged by T1 fingerprint analysis. We will establish the exact relationship between S1, S3 and M by T1 fingerprint analysis of M, by heteroduplex mapping, and by appropriate hybridization experiments. A more complete sequence analysis of S3 will continue with the aid of strand separation, T1 partial digestion, and polynucleotide kinase labelling of T1 oligonucleotides. We will determine whether nuclear mutations affecting the replication of M but not of L also affect the replication of S dsRNAs (by genetic experiments) and whether the S dsRNAs are encapsidated in particles containing the same polypeptides as those containing L and M (by immunological experiments). Transcription of the killer RNAs will be investigated by isolation of polysomal single-stranded RNAs hybridizing to denatured killer dsRNAs or to the separated strands of killer dsRNAs, followed by 5' and 3' end group analysis. We will continue attempts to demonstrate RNA-dependent RNA synthesis in killer VLPs or in VLPs in the presence of possible host factors. The intraviral state of the killer RNAs will be investigated by electron microscopy of disrupted particles.